Beam Size Calculator
Calculate the required beam size for your span and load. Find suitable built-up and solid timber beam options.
How to Use This Calculator
Beams carry loads from joists to posts or walls. Sizing depends on the span, tributary area, and load type. This calculator helps you find suitable beam sizes for your application.
- Enter the beam span (distance between supports).
- Enter tributary width (half the joist span on each side of beam).
- Select load type (floor, deck, roof, or balcony).
- Choose beam type preference (built-up or solid timber).
- Review recommended sizes and their utilization percentages.
Why This Matters
Beams are critical structural elements. Undersized beams cause sagging, bouncy floors, and potential structural failure. Oversized beams waste money and may be difficult to handle. Proper sizing ensures safe, comfortable structures that meet building codes.
- Find minimum beam size for your load
- Compare built-up vs solid timber options
- See utilization percentages for sizing margin
- Understand load calculations
- Select economical yet adequate sizes
Worked Examples
Floor Beam
12-foot span beam supporting joists spanning 8 feet on each side (16' tributary).
Deck Beam
8-foot span beam with joists spanning 6 feet each side (12' tributary).
Roof Ridge Beam
14-foot span supporting 10 feet of rafter length each side.
Common Mistakes to Avoid
- Forgetting tributary width - the beam supports area, not just the joists directly above it.
- Using nominal dimensions for calculations - a 4x8 is actually 3.5" x 7.5".
- Ignoring deflection criteria - beams must be stiff enough to prevent bounce.
- Not accounting for point loads - concentrated loads require separate analysis.
- Improper built-up beam construction - boards must be properly nailed per code.